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Reduce liquid manure storage with wastewater irrigation system

Progressive Dairyman Editor Karen Lee Published on 10 January 2017

Liquid manure can be costly to handle and haul long distances, causing dairy farms to consider alternative options to just storing everything in a lagoon.

One option offered by Terry Mescher, an agricultural engineer with the Ohio Department of Agriculture, is to install an in-place irrigation system for milkhouse or parlor wastewater. This keeps the wastewater from diluting the farm’s manure.

“We’ve been using [in-place irrigation systems] successfully on milkhouse water for probably about 10 years now. They do relatively well for us once we get beyond some of the maintenance issues,” Mescher said during a presentation at the 2016 North American Manure Expo in London, Ohio.

“The systems are fairly simple, reliable and allow the owner to avoid a liquid manure storage system,” he added.

For now, it is best suited for smaller wastewater flows, ideally 400 to 600 gallons per day, and should only be used for fairly low nutrient content water since it will always be applied to the same patch of land.

The system consists of a settling tank, effluent filter, dosing tank, pump, irrigation line, standpipe and impact nozzle.

Settling tank

The settling tank is used to drop the solids out and float the fats and oils along the top. It is typically designed to hold five days’ worth of wastewater to allow the settling to occur before it moves through the next step.

Effluent filter

An effluent filter is located at the outlet of the settling tank to remove and reduce the amount of solids heading to the dosing tank. “We’ve got a pump that will take some solids, but if we start to get extreme material in there or start to get fats and oils running across there, the pump’s not going to work very well and our irrigation nozzles are going to plug up fairly quickly,” Mescher said.

Dosing tank

The dosing tank is a precast holding tank. Mescher said he uses one without baffles because they can get in the way when trying to service the pump. This tank should be sized for a minimum three-day dosing interval. It is best to irrigate every three to five days to give the plants time to dry off and recover before sprinkling them again.

In addition, there should be enough space in the dosing tank to maintain a liquid level capable of cooling the pump.

Pump

The pump in this system has to develop pressure to drive the water through a pipeline and out an irrigation nozzle. “The irrigation nozzles that we use usually require somewhere in the range of 25 to 30 psi out of the nozzle,” Mescher said. “So when we’re talking about the pump’s capacity, we need 30 to 35 psi of pump discharge to overcome the pipe losses, the elevation difference and supply the 25 psi at the nozzle.”

Gallons per minute also needs to be part of the equation. Each nozzle will throw about 20 to 25 gallons per minute. If there are two nozzles, the system needs to be able to deliver 45 to 50 gallons at a pressure of 30 to 35 psi.

“The pump is the driving force behind all of this, and if the pump isn’t working right, the system’s going to fail,” Mescher said.

There are three floats to help turn the pump on and off – an on float, an off float and a high-water level float that flips on a light to notify the operator that there is a problem.

Mescher said he saw a lot of problems from the floats early on, but has since switched to using sealed mercury float switches and resolved most of those problems.

He commonly uses a 2 horsepower pump with a minimum 2-inch discharge to provide the capacity needed by the system. Mescher also strongly recommended installing a pump disconnect to pull the entire pump out instead of sending someone into the tank to service it. The tank may either be full of water or contain hazardous gases if recently emptied.

Irrigation line

For the irrigation line, his specifications call for Schedule 40 PVC for all of the pipe and Schedule 80 PVC for all connections. His typical system calls for 3 or 4 inch diameter pipes and fittings, depending on the length of the line. Thus far he has installed systems from 100 feet of line to 1,200 feet.

Mescher said a heavy-duty waterline could be used if it’s available, but he fears it might collapse without constant pressure, which this system does not provide.

The irrigation line should run uphill to allow the water to drain back to the pump. There should also be a small hole drilled in the vertical line from the pump to the irrigation line so the return water can drain out. This lets the water escape from the line so it won’t freeze and plug the line during winter.

The line should have a minimum 18 inches of cover, which won’t prevent freezing, but will protect it from animals, traffic and a bit of weather protection.

Standpipe

Mescher uses a 1 1/4-inch galvanized pipe to mount the irrigation nozzle. The galvanized material can withstand the strain of throwing the water out 60 to 70 feet. “Early on, we always insulated [the standpipe], but really I don’t know how necessary it is,” he said. “We’ve had some that have insulated it, some that have not. I don’t know that it is that important, but it might make us feel better about the winter.”

The typical height of the standpipe is 4 to 5 feet above the ground, which helps get the water out across the top of corn. However, he said it doesn’t have to be that high depending on what is in the irrigation area.

Impact nozzle

He suggested using a brass impact sprinkler with a nozzle size of 7/16-inch or 3/8-inch. They are expensive, Mescher said, but they don’t corrode and are high enough quality to put up with the wastewater freezing and thawing, whereas plastic nozzles have struggled in those conditions.

A smaller irrigation nozzle would allow for a smaller pump, but may lead to more problems with plugging.

Application area

The land to be irrigated needs to have 100 percent cover all year to meet NRCS standards. “Typically, I put half of that area in grass, and the other half can be a crop, or the whole thing can be a pasture,” he said.

He sizes the application area to apply 0.1 inch of water with every dosing event. For the soils in his area of west central Ohio, he can apply 0.2 inch of water at a time, but Mescher cuts that in half to allow a farmer to limit the irrigation area by half depending on the crop cycle and to allow for farm expansion. “[The farm] can increase that wastewater production without negatively impacting my system,” he said.

It is important to establish the grass in the application area before starting the rest of the project. “Plant the grass before you’re going to start digging the tank,” he said. “As soon as we get that all installed, we’re going to want to turn it on, and we cannot establish that grass if we’re starting to pepper it with wastewater.”

Management considerations

There are a few areas of management to be considered when using this system. The first is minimizing the solids coming into the system from the parlor. Solid manure should be scraped from the parlor before it is washed down with water.

“Solids that usually get us are things like gravel and little bits of corn when we have a whole bunch of that manure going in the system. That’s what makes it through the pump, makes it through the effluent filter and plugs up our nozzles,” Mescher said.

Water from plate coolers should not be sent through this system simply because of its sheer volume. “Those plate coolers are usually putting out somewhere between 600 and 1,000 gallons of water per day. We’re gearing these systems for 400 to 600 gallons per day, so we’ve got to find a different home for plate cooler water,” he said.

He also did not recommend incorporating any holding pen wash down water either, due to the amount of volume it can be.

System maintenance

The settling tank must be pumped out periodically. At start up, he recommended pumping it every three months to see what type of buildup is occurring. In addition, it takes awhile for bacteria to build in the first tank, so the solids won’t digest as well at the onset. Once it gets going, he said most operations could pump it out once or twice a year.

The effluent filter should be cleaned when the tank is pumped. It will plug fairly often the first couple of months until the bacteria are present to eat away at the fats and oils.

He said the float control panel could be “extraordinarily sensitive to any kind of a voltage surge.” Lightning in the area can cause system failures, but extra grounding seems to help with that.

The electrical panels are also really sensitive to corrosion from any gases coming back out of the dosing tank. He recommended the use of plumber’s putty to seal the conduit that runs from the dosing tank to the electrical panel.

If the pump must be turned on and off during installation or maintenance, Mescher said it is important to leave the pump off until the irrigation line is completely drained. Otherwise, you could create a water hammer that will blow the connections apart.

During installation, Mescher said to leave the nozzles in the box for the first 10 to 14 days to give the system a chance to purge. “It’s going to make a mess, I understand that,” he said, “but if you put those irrigation nozzles on there, the first time you use it, you’ll always have gravel, straw, buildup right behind the little nozzles. It causes a lot of headaches.”

Since the irrigation nozzles run every three to five days, 365 days a year, they will operate in freezing temperatures (depending upon your climate) and may freeze in place. After the water runs for several minutes, it should thaw the nozzle, and it will start to rotate again. If it is stuck in place for days on end, Mescher said to check its tightness because it may have been installed incorrectly.

System cost

The cost of the system can vary depending on the dosing and the length of the line; however, Mescher said the typical range is from $12,000 to $20,000. This includes everything from the tanks and lines to pump and nozzles, even the excavation. He added that the pumps could be expected to last five to seven years.

While a few maintenance issues can be expected, an in-place wastewater system is one option to keep smaller dairy farms from having to manage a liquid manure system.  end mark

Karen Lee
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